DESCRIPTION (Taken from application) The overall goal of this research is to gain an understanding of the transport and degradation mechanisms involved in soil bioremediation systems at Superfund sites. Determining the role of biofilms in bioremediation of sites contaminated with toxic organics, such as polycyclic aromatic hydrocarbons (PAHs), is crucial to designing more efficient treatment systems. We propose to elucidate the properties of soil biofilms used to remediate soils contaminated with PAHs and to develop engineered biofilm processes that enhance bioavailability and biodegradation kinetics. The findings should also be applicable to bioremediation of other toxic organics. The primary intent is to develop a fundamental understanding of the role of biofilms in soil bioremediation systems, in terms of biofilm growth and structure and the role of the biofilm on mass transport to the biofilm microorganisms responsible for the contaminant biodegradation. A particularly salient aspect of this research is that it will address not only bioremediation of individual compounds, but also mixtures of toxic compounds with a range of recalcitrance. This research will include definition of soil biofilm characteristics, the role of the biofilm exopolymer matrix in transporting nutrients and contaminants to biofilm microorganisms or in retarding their movement, and development of innovative PAH bioremediation processes that maximize the useful properties of soil biofilms. Specific aims include: (1) assessing the abiotic and biotic fates of PAHs in soils, including sorption/desorption kinetics, distribution coefficients and biodegradation; (2) characterizing the physical structure of soil biofilms growing in the presence of toxic organics using light and confocal scanning laser microscopy, the chemical characteristics of the biofilms using microelectrodes, and the distribution and diversity of PAH degrading microorganisms in the biofilm; (3) determining the degree of detoxification of PAHs in soils using Microtox and mutagenicity testing procedures; and (4) developing innovative soil remediation systems utilizing either pulsed injection of nutrients or creation of a soil biowall.